The invention further relates to an apparatus for carrying out the process.
In a known process (British patent specification No 744 742) for gasifying a fine-grain gasification material and/or for reforming a carbon dioxide-bearing gas to provide a carbon monoxide-bearing gas, the reactor is supplied with the heat required for the chemical reaction to take place, by way of fine-grain heat-carrier particles which are passed in a closed circuit and which are heated outside the reactor. In the case of particles which are conveyed in counter-flow relationship, the endeavour is to achieve good distribution of the particles in the reactor and thus good transfer of heat between the particles and the gasification substance, by virtue of the reactor being arranged horizontally and rotated about its longitudinal axis. Particles which reach the bottom of the reactor are lifted by the rotary movement in order then to fall back to the bottom of the reactor, due to their own weight; that arrangement is intended to cause the interior of the reactor to be acted upon by the particles, in a similar manner to a trickle flow therewithin, in order to give a good heat exchange effect. For particles which move in co-flow relationship, it is proposed that they are conveyed from an upper region of a vertically disposed reactor through a layer of fine-grain solid gasification substances to the bottom of the reactor from which they are discharged together with any ash which is produced.
The particles consist of metals or metal oxides and are about between 1 and 5 mm in grain size. Any ash which is discharged by way of the particles is separated out before the particles are recycled to the heater, for example by sieving or by magnetic separation of ash components. The heater provided for heating the particles likewise comprises a heater cylinder which rotates about its longitudinal axis; the aspect of the supply of heat to the heater is not discussed in detail. The particles which are heated in the heater are passed to the heater again, within the closed circuit, after they issue from the reactor by way of a coking device or an air preheater. When gasifying substances in dust form, they can assume a floating condition within the reactor, in a manner which is not described in further detail.
The use of a rotating reactor and also a rotating heater means that the level of expenditure involved in carrying the process into effect is relatively high. A corresponding level of expenditure is required for constructing and maintaining an apparatus for carrying out the process. In addition, there is no guarantee of intimate mixing with the gasification substance, either when the particles pass with a trickle flow through the gasification substance when the reactor rotates, or when a layer of the gasification material within a rotating reactor is acted upon by downwardly moving particles, so that the level of efficiency in terms of heat exchange is relatively low.
In a known process for reforming of gases containing CO.sub.2 and H.sub.2 O, and hydrocarbon-bearing gases to provide reduction gases with a high H.sub.2 and CO component (German patent specification No 2 947 128), the heat transfer medium used is fluidisable heat-resistant particles, for example of aluminium oxide, of a particle size in the range of between 50 and 500 .mu.m. There is no provision therein for gasification of liquid or solid gasification substances. For the purposes of reforming gases, the particles which circulate in a closed circuit firstly absorb in the heater and in the combustion chamber, the heat of combustion gases which are produced in the combustion chamber. For that purpose the particles are held in a fluidised bed which is formed with the combustion gas, both in the heater and also in the combustion chamber, in each case above a respective grid. In that situation they pass by way of a down pipe from the heater into the combustion chamber from which they pass by way of a further down pipe into a bottom chamber which is disposed beneath the combustion chamber. The bottom chamber is connected by way of a conveyor pipe to the upper region of the reactor in which the particles are received above grids in fluidised beds formed with the gas to be reformed. The fluidised beds produced in the reactor are likewise connected by way of a down pipe. In order to prevent reduction gas produced in the reactor from passing into the bottom chamber or the combustion chamber, arranged in the conveyor pipe is a double-acting valve which is to open or close alternately. The double-acting valve provides on the one hand that particles are discontinuously fed to the reactor while on the other hand it means that the structure and operation of the apparatus for carrying out the process are relatively expensive and involve an increased amount of wear and accordingly also an increased susceptibility to trouble.